Micro-Electro Mechanical Systems (MEMSs) are a type of integrated devices used for acquiring information, processing information, and executing operations, etc. Sensors are a typical type of MEMS devices; and are referred as MEMS sensors. MEMS sensors are able to receive certain types of external information, such as pressure, position, velocity, acceleration, magnetic field, temperature, and humidity, etc. Further, the MEMS sensors are also able to covert the external information into electrical signals such that the external information can be processed in a computer system. The typical MEMS sensors include temperature sensors, pressure sensors, and humidity sensors, etc.
In order to obtain the external information, a cavity is often formed in a MEMS device to connect with the external environment. The external liquid or gas is able to enter into the cavity. Thus, the information of the gas or liquid entering into the cavity, such as pressure, temperature, or humidity, etc., is obtained.
FIG. 1 illustrates a semiconductor structure having a cavity. The semiconductor structure is used as a humidity sensor. The semiconductor structure includes a single crystal silicon substrate 100; and a silicon oxide layer 101 formed on the surface of the single crystal silicon substrate 100. Two openings 102 penetrating through the silicon oxide layer 101 are formed in the silicon oxide layer 101. The semiconductor structure also includes a cavity 103 formed in the single crystal silicon substrate 100 under the silicon oxide layer 101 and between the two openings 102.
The silicon oxide layer 101 is a humidity sensitive material. With the changing of the humidity of the air entering into the cavity 103, the dielectric constant of the silicon oxide layer 101 changes correspondingly. By measuring the dielectric constant of the silicon oxide layer 101, the humidity of the air is obtained.
However, the morphology of the cavity formed by existing methods may not match designed requirements. Thus, information obtained by the MEMS having the cavity may be inaccurate. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.